1. Field of the Invention
The present invention relates to a dryer for drying items in a rotating drum and to a method of controlling a dryer.
2. Description of Related Art
Rotating drum dryers are now well known. Items to be dried, such as clothing, sheets, etc. are loaded into a rotatable drum. The drum is rotated and hot air is forced into the drum. The hot air is generated by a hot air generation system generally including a heater and a fan. During the drying operation, the rotating drum is rotated by a motor.
A conventional dryer has an exhaust temperature sensor for detecting the temperature of air being exhausted from the rotating drum. The detected temperature is used to determine a drying operation time period. The dryer detects the exhaust temperature at the beginning of a drying operation and then again some time later. Based on the temperatures detected, there is determined a rate of increase of exhaust temperature. The drying operation time period is determined in accordance with the rate of increase in exhaust temperature. For example, if the exhaust temperature increases slowly, the drying operation time period is made longer. However, if the exhaust temperature increases rapidly, the drying operation time period is shortened.
However, such a method of controlling the time period is inadequate. When clothes are washed in hot water immediately before drying and are then immediately put into the rotating drum they are still warm from the wash. The exhaust temperature will rise faster than it would otherwise do when the clothes are not already warm from a hot water wash. The warm clothing "fools" such a system into making the drying operation time period too short.
Another known dryer has a dryness detecting device for detecting the degree of dryness of items being dried in the rotating drum. The dryer also has an amount detecting device for detecting the amount, or weight, of the items being dried. The drying operation time period is determined in accordance with the detected degree of dryness and/or amount of items. This type of dryer usually ends its drying operation when the degree of dryness reaches a predetermined level. Such dryers are described in the U.S. Pat. No. 4,738,034. The dryness detecting device and the amount detecting device described in U.S. Pat. No. 4,738,034 commonly use detection electrodes. These electrodes are arranged to face the interior of the rotating drum so that they can come into contact with clothes in the rotating drum being dried. The dryness detecting device includes a dryness detecting circuit for detecting a degree of dryness based on the electrical resistance of the clothes coming into contact with the electrodes while the drum is rotating. The amount detecting device has an amount detecting circuit for detecting the amount of clothes based on the frequency with which clothes in the drum come into contact with the electrodes. The dryer described in the U.S. Pat. No. 4,738,034 determines the end of the drying operation based on the degree of dryness detected by the dryness detecting device and/or the amount of clothes detected by the amount detecting device.
Although the known dryers described above perform adequately under ideal conditions, they do not function properly when drying large items, such as bathrobes, sheets, etc. particularly when they are mixed with regular items of clothing. The regular items of clothing often become tangled with the large items or wrapped by them. When such tangles occur, the outer parts of the items receive a good supply of hot air and dry quickly. In particular, clothes positioned close to the hot air supply port receive concentrated hot air and dry quickly. The outer parts of the clothes in the tangled or wrapped state make contact with the electrodes. Therefore, the electrodes detect a high degree of dryness and the dryer ends the drying operation prematurely. However, the inner parts of clothes that are tangled do not receive much hot air flow.